State St. and Wharf St. Bioswale

About Bioswales

Bioswales are shallow, landscaped ditches designed to filter out sediment and other pollutants out of runoff as they move water from one point to another. Basic bioswales are a gently sloping ditch planted with grass which are designed to slow the water down enough to allow sediment to settle out. Some newer bioswales have a layer of prepared soil (sand, soil, and compost), with sand, crushed rock, and gravel underground, and are planted with hardy native plants that can tolerate both wet and dry conditions. After the runoff has been filtered through plants and soil, treated water flows downstream.

Water Quality Benefit: Bioswales help improve water quality by slowing and filtering stormwater. Living material in the plants and soil captures and biologically degrades pollutants, while absorbing some nutrients, but generally does not treat dissolved metals.

Water Quantity Benefit: When possible, some bioswales are designed for infiltration. In areas where the soil allows water to soak in, bioswales slow the speed of the runoff to reduce flooding, while recharging groundwater. The plants in bioswales also soak up some water which then evaporates during the growing season.